This invention relates to a method of manufacturing an electrode system comprising at least two conductors positioned at a predetermined distance from each other by means of insulation material, in which burrs, if any, of the facing parts of said conductors are removed by applying an electric potential difference between the conductors, said difference being sufficiently large to generate an electric flash-over between the conductors.
The invention furthermore relates to an electrode system manufactured by using this method.
The term "electrode system" is to be understood to mean herein a system of electric conductors between which a strong electric field is generated in operating circumstances, for example, in electron gun systems, color selection electrodes with post-focusing effect for color display tubes and also printed circuit boards on whch conductive tracks extending closely beside each other are provided.
In electrode systems, such as, electron gun systems for cathode ray tubes, stringent requirements are imposed upon the high voltage stability of the electrode system. This means that the possibility of the occurrence of an electric flash-over between electrodes situated at a short distance from each other should be minimized in normal operating circumstances of the electrode system. In fact, such flash-overs may damage not only the electrode system itself but also the electronic circuit connected thereto. The cause of these flash-overs usually is mechanical imperfections of the electrode system, for example small burrs or loose particles present on the electrodes. It is therefore necessary to remove said burrs and loose particles from the electrodes before ultimately putting the electrode system in operation.
According to a conventional method, said burrs and loose particles are removed by applying, in the last or in one of the last phases of the manufacturing process of the electrode system, an electric potential difference between electrodes which are situated at a short distance from each other, said difference exceeding the voltage difference at which said electrodes are operated in normal operating circumstances. If a flash-over occurs, it will usually occur at the area of a burr or loose particle, as a result of which the burr or the loose particle is melted away or burnt away, so that the source of further flash-overs at that area has been removed. This process, sometimes termed "arc out process", usually takes place in a vacuum. During this arcing out, however, metal is sputtered which may deposit on electrically insulating parts of the electrode system. This has for its result that electric conductivity can take place via the walls of said insulating parts, which is undesirable. This is a problem in particular in electrode systems in which the insulation path along the insulating material between the electrodes is particularly short. Such an electrode system is disclosed, for example, in British Patent Specification No. 1.496.949. This specification described a colour display tube of the post-focussing type. In this case the colour selection electrode situated at a short distance before the display screen consists of two substantially flat electrode structures which are kept spaced at a distance of approximately 100 to 200 .mu.m by means of insulators situated between the electrode structures. The two electrodes are provided with a plurality of apertures which are aligned two by two and through which pass the electron beams generated by an electron gun. The two electrode structures are operated at an electric potential difference of approximately 1000 to 2000 volts so as to exert in the apertures a focusing effect on the electron beams. Arcing out such an electrode system in a vacuum has proved to be an unfit method since the small deposit of sputtered metal on the insulators makes the colour selection electrode unfit for further use. Deposition of sputtered metal causes a problem in particular when a synthetic resin is used as an insulation material. Electric conductivity along the surface of the insulator then results in a local heating of said surface so that decompositon and carbon formation of the synthetic resin occurs. As a result of this the electric conductivity will increase and ultimately a complete short circuit is formed between the two electrode structures.